How a solenoid valve is works? - Part 2

How a solenoid valve is works? - Part 2
1. Direct-acting solenoid valve

• Working principle
  When the power is on, the solenoid coil generates the electromagnetic force to lift the closure member from the valve seat to open the valve. When the power is cut off, the electromagnetic force disappears and the spring presses the closure member on the valve seat to close the valve.
• Characteristics
  It can work normally in the vacuum, negative pressure and zero pressure. However, the diameter normally doesn’t exceed 25mm.

2. Pilot-operated solenoid valve

• Working principle
  When the power is on, the electromagnetic force opens the pilot hole and the pressure of the upper chamber decreases rapidly, forming a pressure difference which is low in the upside and high in the bottom around the closure element. The fluid pressure promotes the closure element to move upwards to open the valve. When the power is off, the spring force closes the pilot hole. The pressure through the bypass port rapidly forms a pressure difference which is high in the upside and low in the bottom around the closure element. The fluid pressure drives the closure element to move downwards and close the valve.
• Characteristics
  The fluid pressure scope has a relatively high upper limit. It can be installed randomly, with the fluid pressure difference condition being satisfied.